Devices and methods for controlling movement of an electrosurgical electrode

ABSTRACT

An electrosurgical electrode assembly having a cutting device including a catheter with a proximal and distal end, and an electrode carried on the distal end of the catheter. A controller is connected to the cutting device. A data acquisition system is connected to the controller and is capable of monitoring voltage and current output. A microprocessor may also be connected to the data acquisition system for processing voltage and current data from the data acquisition system. A generator is also connected to the data acquisition system. The controller initiates movement of the electrode upon arc initiation at the electrode. Methods of using the devices herein are also disclosed.

This application is a continuation of U.S. application Ser. No.11/433,272, filed on May 11, 2006, which is a continuation of U.S.application Ser. No. 11/003,267, filed on Dec. 2, 2004, now abandoned,which is a continuation-in-part of U.S. application Ser. No. 10/714,126,filed Nov. 13, 2003, now issued as U.S. Pat. No. 7,060,063, which claimspriority to U.S. Provisional Application Ser. No. 60/426,030, filed onNov. 13, 2002. This invention relates to devices and methods that may,but do not necessarily, involve the use of a target tissue localizationdevice, such as shown in U.S. application Ser. No. 09/677,952, filedOct. 2, 2000, now issued as U.S. Pat. No. 6,325,816, in conjunction withan electrosurgical loop-type cutter, such as shown in U.S. applicationSer. No. 09/844,661, filed Apr. 27, 2001; U.S. application Ser. No.09/588,278, filed Jun. 5, 2000, now issued as U.S. Pat. No. 6,530,923;and U.S. application Ser. No. 10/045,657, filed Nov. 7, 2001. All of theabove-mentioned patents and applications are herein expresslyincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to an electrosurgical electrodesystem that is capable of excising a tissue sample using a systemenhanced by impedance feedback during the movement of the cuttingelement.

BACKGROUND

Typical electrosurgical procedures, such as cutting or cauteryprocedures, are performed with a hand held device, which the user canmanipulate as the RF energy is delivered in order to facilitate thecreation of the desired effect at the electrode. The ability to visuallysee the electrode and to change the proportion of the electrode that isheld in contact with the tissue allows the user to adjust the motion orposition of the device with respect to the activity observed at theelectrode to compensate for the constant power output of a commercialelectrosurgical generator and to force the generator to achieve thedesired effect. With a percutaneous procedure, in particular anautomated, percutaneous procedure, this type of user-based control isnot possible, since the electrode is, in many cases, not visible. And inthe case of automated control, the effects occur too quickly to allowhuman reaction. In this case, it is advantageous to have an automatedmethod to evaluate the effect at the electrode and a method to determinewhen specific events have occurred and initiate the appropriate action.Of specific concern in a procedure requiring the cutting or excision oftissue is the creation of an arc at the electrode, since an arc permitsthe vaporization of tissue, which is the phenomenon that creates thecut.

For manual systems, where the cutting loop is deployed and rotated byhand by the user, other problems exist. The user may not know if theelectrode movement is too slow, which leads to too much RF energyexposure that can result in excessive thermal damage and/or vaporizationof the intended tissue sample. If, on the other hand, the electrodemovement is too fast, this could result in a weak cutting arc or totalloss of the cutting arc, which could result in undersized ormechanically damaged specimens.

This invention utilizes the measurements of the electricalcharacteristics of the tissue and correlates them to a physical effectat the electrode, which is then used to signal the user to makeappropriate adjustments in the method.

SUMMARY OF THE INVENTION

The present invention relates to devices and methods for using anelectrosurgical electrode to excise a tissue sample from a patient. Moreparticularly, the invention provides a system that includes a means formonitoring the appropriate time to initiate movement of the cuttingdevice.

In one embodiment, the electrosurgical electrode assembly includes acutting device having a catheter with a proximal and distal end. Thecutting device also has an electrode carried by the distal end of thecatheter. The proximal end of the cutting device is a handpiece that maybe reusable or disposable, or a combination thereof. In particular, thehandle of the handpiece may be reusable and the electrode inserted intothe handle may be disposable. A controller is connected to the cuttingdevice. A data acquisition system is connected to the controller that iscapable of monitoring voltage and current output. The system alsocontains a microprocessor connected to the data acquisition system,which is capable of processing voltage and current data from the dataacquisition system. An electrosurgical generator is also connected tothe data acquisition system. In operation, the controller initiatesmovement of the electrode upon arc initiation at the electrode.

In another embodiment, the system also includes an electrically isolatedswitch connecting the data acquisition system and the controller. Theelectrically isolated switch may be an optical switch.

In another embodiment, the controller, data acquisition system,electrosurgical generator, and microprocessor are integrated into asingle control unit. The control unit may be able to drive DC motorsthat are located in the reusable handpiece of the cutting device.

In another embodiment, the electrosurgical electrode assembly includes acutting device having a catheter with a proximal and distal end. Thecutting device also has an electrode carried by the distal end of thecatheter. The proximal end of the cutting device is a handpiece that maybe reusable or disposable, or a combination thereof. In particular, thehandle of the handpiece may be reusable and the electrode inserted intothe handle may be disposable. A controller is connected to the cuttingdevice. A data acquisition system is connected to the controller that iscapable of monitoring voltage and current output. The data acquisitionsystem is providing feedback information to the controller through thearc detection cable. An electrosurgical generator is also connected tothe data acquisition system. The output from the electrosurgicalgenerator passes through the data acquisition system and the controllerto the patient through the handpiece. In operation, the controllerswitches on the electrosurgical energy to the electrode and initiatesmovement of the electrode upon arc initiation at the electrode based onfeedback information from the arc detection cable. In an alternativeembodiment, the system may also include a microprocessor connected tothe data acquisition system. The microprocessor may include logic tocalculate the load (or electrical) impedance so that it may determinethe presence of an arc.

In yet another embodiment, the electrosurgical electrode assemblyincludes a cutting device having a catheter with a proximal and distalend. The cutting device also has an electrode carried by the distal endof the catheter. The proximal end of the cutting device is a handpiecethat may be reusable or disposable, or a combination thereof. Inparticular, the handle of the handpiece may be reusable and theelectrode inserted into the handle may be disposable. The assembly alsoincludes a control unit connected to the cutting device. This integratedcontrol unit contains an electrosurgical generator connected to thecutting device and a data acquisition system connected to the generatorthat is capable of monitoring voltage and current output. The controlunit also contains a microprocessor connected to the data acquisitionsystem, which is capable of processing voltage and current data from thedata acquisition system, and a controller connected to the dataacquisition system. In operation, the controller initiates movement ofthe electrode upon arc initiation at the electrode.

In another embodiment, the microprocessor of the systems described aboveincludes logic to calculate the load (or electrical) impedance from thecurrent and voltage output. By monitoring the change in the load(electrical) impedance value, the presence of an arc can be determined.The presence of the arc could also be determined by monitoring any one,or a combination, of the following electrical characteristics:electrical impedance, a change in electrical impedance, voltage, achange in voltage, current, or a change in current.

In another embodiment, the systems include a return electrode connectedto the electrosurgical generator.

In yet another embodiment, the electrode has a proximal part and adistal part. The distal part of the electrode is movable between aretracted state and an outwardly extending operational state. A firstdriver may also be operably coupled to the electrode, where the firstdriver can move the electrode from the retracted state and/or rotate theelectrode about its axis in order to separate a tissue section from thesurrounding tissue by moving the electrode. In addition to rotating theelectrode, the electrode may also be moved translationally or in anyother way to effect separation of the tissue section from thesurrounding tissue.

The methods of the present invention relate to controlling the initialmovement of an electrosurgical electrode. Energy is delivered to anelectrosurgical electrode. The electrical characteristics associatedwith the electrosurgical electrode are then monitored. This monitoringstep may include monitoring any one, or a combination, of the followingelectrical characteristics: electrical impedance, a change in electricalimpedance, voltage, a change in voltage, current, or a change incurrent. The initiation of an arc is then determined based on themonitoring step. The electrosurgical electrode is then moved once thearc has been detected. In one embodiment, the electrode may be movedautomatically once the arc has been detected. The energy being deliveredto the electrosurgical electrode may then be adjusted based upon themonitoring step in an effort to help maintain an effective arc. Inaddition, the speed of the electrosurgical electrode may also beadjusted based on the monitoring step in an effort to help maintain aneffective arc.

The methods of the present invention also relate to controlling theoperation of a percutaneously-placed electrosurgical electrode of anelectrosurgical device. Energy is first delivered to apercutaneously-placed electrosurgical electrode to create an arc at thatlocation, while the electrode is stationary. The electricalcharacteristics associated with the electrosurgical electrode are thenmonitored. The electrical characteristic being monitored may be any one,or a combination, of the following: electrical impedance, a change inelectrical impedance, voltage, a change in voltage, current, or a changein current. Once the creation of a cutting arc is established betweenthe adjacent tissue and the electrode, the controller initiates movementof the electrode to effect separation of the tissue section from thesurrounding tissue. The energy being delivered to the electrosurgicalelectrode may then be adjusted based upon the monitoring step in aneffort to help maintain an effective arc.

In another method of controlling the operation of apercutaneously-placed electrosurgical electrode of an electrosurgicaldevice, the percutaneously-placed electrosurgical electrode may be movedalong a predetermined path while energy is being delivered. Anelectrical characteristic associated with the electrode may be monitoredat the electrode. The electrical characteristic being monitored may beany one, or a combination, of the following: electrical impedance, achange in electrical impedance, voltage, a change in voltage, current,or a change in current. An expected position of the electrode along thepredetermined path may also be monitored. The energy delivered to theelectrode may then be adjusted based on the monitoring steps of theelectrical characteristic and expected position in order to maintain aneffective arc. In one embodiment, the electrical characteristic beingmonitored is electrical impedance.

In another method for controlling the movement of an electrosurgicalelectrode of an electrosurgical device within a target tissue, theelectrosurgical electrode may be inserted into the target tissue. Energyis delivered to the electrosurgical electrode, which is then moved tocut the target tissue. The electrosurgical electrode can be rotated,translated, or any combination thereof, in order to accomplish thecutting of the target tissue. The electrode may be moved eitherautomatically or manually. In another embodiment, the electrode is movedmanually. An electrical characteristic associated with theelectrosurgical electrode is monitored while the electrode is moved. Thespeed of the electrosurgical electrode can be adjusted based on themonitoring step in order to maintain an effective arc. The electricalcharacteristic being monitored may be any one, or a combination, of thefollowing: electrical impedance, a change in electrical impedance,voltage, a change in voltage, current, or a change in current. In apreferred embodiment, electrical impedance or a change in electricalimpedance is monitored. The method may also include the step ofproviding feedback to a user based on the monitoring step, wherein theuser can adjust the speed based on the feedback. Alternatively, in anintegrated system, the speed may be automatically adjusted based on thefeedback. The feedback can comprise audio feedback, visual feedback, orany combination. Furthermore, the energy delivered to theelectrosurgical electrode may also be adjusted based on the monitoringstep in order to maintain an effective arc. The electricalcharacteristic may also be monitored to determine when an arc has beeninitiated before moving the electrode.

In another method for controlling the movement of apercutaneously-placed electrosurgical electrode of an electrosurgicaldevice within a target tissue, the electrosurgical electrode may beinserted into the target tissue. Energy is delivered to theelectrosurgical electrode to create an arc threat while moving theelectrode to cut the target tissue. The electrosurgical electrode can berotated, translated, or any combination thereof, in order to accomplishthe cutting of the target tissue. The electrode may be moved eitherautomatically or manually. In a preferred embodiment, the electrode ismoved manually. An electrical characteristic associated with theelectrosurgical electrode is monitored while the electrode is moved. Thespeed of the electrossurgical electrode can be adjusted based on themonitoring step in order to maintain an effective arc. The electricalcharacteristic being monitored may be any one, or a combination, of thefollowing: electrical impedance, a change in electrical impedance,voltage, a change in voltage, current, or a change in current. In apreferred embodiment, electrical impedance or a change in electricalimpedance is monitored. The method may also include the step ofproviding feedback to a user based on the monitoring step, wherein theuser can adjust the speed based on the feedback. Alternatively, in anintegrated system, the speed may be automatically adjusted based on thefeedback. The feedback can comprises audio feedback, visual feedback, orany combination. Furthermore, the energy delivered to theelectrosurgical electrode may also be adjusted based on the monitoringstep in order to maintain an effective arc. The electricalcharacteristic may also be monitored to determine when an arc has beeninitiated before moving the electrode.

As discussed above, the devices of the present invention monitor anelectrical characteristic of the electrosurgical electrode duringinitiation of the arc. The electrical characteristic being monitored maybe any one, or a combination, of the following: electrical (or load)impedance, a change in electrical (or load) impedance, voltage, a changein voltage, current, or a change in current. In a preferred embodiment,the system monitors for an electrical impedance value over 500 ohms. Inanother preferred embodiment, the system monitors for an electricalimpedance value over 2-times a baseline electrical impedance value. Thiselectrical impedance value is measured at very low power, usually belowthe level that is known to create an arc at the electrode. In yetanother preferred embodiment, the system monitors for an electricalimpedance value of 2.5-times a baseline electrical impedance value.

As discussed above, in addition to monitoring an electricalcharacteristic during the initiation of the arc as described above, thedevices of the present invention monitor an electrical characteristic ofthe electrosurgical electrode during the movement of the electrosurgicalelectrode. The electrical characteristic being monitored may be any one,or a combination, of the following: electrical (or load) impedance, achange in electrical (or load) impedance, voltage, a change in voltage,current, or a change in current. In a preferred embodiment, the systemmonitors impedance values to determine if the speed of the electrodeshould be varied. Low impedance values signal that the electrode shouldbe moved slower to avoid losing a good cutting arc. Low impedance valuescan be in the range of about 700-1200 ohms, alternatively between about600-1200 ohms, alternatively below about 800 ohms, alternatively belowabout 900 ohms, alternatively below about 1000 ohms. High impedancevalues are indicative of the establishment of a strong cutting arc.Impedance values above about 1200 ohms, alternatively above about 1300ohms, alternatively above about 1500 ohms, alternatively above about2000 ohms, indicate a strong cutting arc. In some instances, impedancevalues may be in the range of 2500-3000 ohms.

In another embodiment, a manually controlled system could be utilizedaccording to the following steps:

-   (1) Align the electrode at the proper location in the tissue.-   (2) Turn on the RF energy.-   (3) Wait for the system to recognize that a cutting arc has been    created.-   (4) Start manual movement of the electrode.-   (5) Move the device quickly through the tissue, while maintaining    high impedance (e.g., above about 1200 ohms).-   (6) Slow the rotation if the load impedance falls to a level where    the arc is struggling (e.g., 700-1200 ohms).-   (7) Stop the electrode movement if the load impedance falls below    about 700 ohms.-   (8) Resume electrode movement once the load impedance rises (e.g.,    above about 1200 ohms).    Indicator lights on the front panel of the device may indicate to    the user when the speed the should be varied. For example, a green    light may be used to signal to “go” (continue moving the electrode),    where the impedance value is above, e.g., about 1200 ohms. A yellow    light may be used to indicate “slow down,” where the impedance value    is between about 700-1200 ohms. A red light may be used to indicate    “stop,” where the impedance falls below about 700 ohms.

A still further aspect of the invention is directed to a method forcreating a tissue section within surrounding tissue. The method includespositioning a distal end of the catheter assembly at a target locationwithin a breast of a patient. An elongate tissue separator element, atthe distal end of the catheter assembly, is moved to a radiallyextended, outwardly bowed, operational state. Energy is supplied to theseparator element. The separator element is automatically rotated aboutthe axis, following at least the start of the separator element movingstep, so to separate a tissue section from surrounding tissue. A tissueholding element, located at the distal end of the catheter assembly, ismoved from a retracted condition to an extended, tissue engagingcondition. The separated tissue section is surrounded by a tubularbraided element by moving the tubular braided element, located at thedistal end of the catheter assembly, from a proximal, radiallycontracted state to a distal, radially expanded state following theautomatically rotating step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a system for using an electrosurgical electrode.

FIG. 2 depicts a diagram of the IO controller of FIG. 1.

FIG. 3 depicts a diagram of the DAS data acquisition system of FIG. 1.

FIG. 4 depicts an integrated system for using an electrosurgicalelectrode with a fully integrated controller and generator.

FIG. 5 depicts another integrated system for using an electrosurgicalelectrode with a fully integrated controller and generator.

FIG. 6 depicts a front panel of an RF generator.

A still further aspect of the invention is directed to a method forcreating a tissue section within surrounding tissue. The method includespositioning a distal end of the catheter assembly at a target locationwithin a breast of a patient. An elongate tissue separator element, atthe distal end of the catheter assembly, is moved to a radiallyextended, outwardly bowed, operational state. Energy is supplied to theseparator element. The separator element is automatically rotated aboutthe axis, following at least the start of the separator element movingstep, so to separate a tissue section from surrounding tissue. A tissueholding element, located at the distal end of the catheter assembly, ismoved from a retracted condition to an extended, tissue engagingcondition. The separated tissue section is surrounded by a tubularbraided element by moving the tubular braided element, located at thedistal end of the catheter assembly, from a proximal, radiallycontracted state to a distal, radially expanded state following theautomatically rotating step.

DETAILED DESCRIPTION

A first embodiment uses a commercially available RF generator along withan “IO” Control Box that controls the RF output to the electrode orloop-type cutter and contains a stepper motor drive to deploy and rotatethe loop electrode. The RF activation, loop deployment and rotation arean automated sequence controlled by a stepper motor drive unit withinthe IO controller. One activation technique includes actuating the RFfor approximately 400 milliseconds prior to the start of thedeployment/rotation of the loop, in order to allow time for an arc to beestablished at the loop electrode. (There is an additional 100millisecond delay induced by the loop deployment mechanism, for a totaldelay of 500 milliseconds.) This type of open loop operation causes twopotential areas of inefficiency. First, the arc could be created earlyin the 500 millisecond period, causing excessive damage to the tissuewhile the electrode is arcing prior to the start of deployment/rotation.The second, more severe possibility is that the rotation sequence wouldbe started prior to the creation of an arc, causing an incomplete cut ordamage to the loop electrode, resulting in an inadequate tissue samplebeing obtained.

To provide more repeatable performance, the creation of a closed-loopsystem has been proposed. Review of the data collected from bothclinical and bench testing has indicated that there is a significantdifference in the load impedance when the electrode is arcing and whenit is merely delivering RF energy to the tissue. This is probably theresult of two different factors, the first being the desiccation oftissue surrounding the electrode (and removal of electrolytic solution)and the second being the creation of a gas-filled space around theelectrode. By monitoring the load impedance during operation, a devicecould be constructed that detects when an arc has been created, andcould initiate the deployment/rotation of the loop electrode.

As depicted in FIG. 1, the first embodiment makes use of the ArtemisData Acquisition System (“DAS”) 10, Artemis Medical, Inc., Hayward,Calif., validated hardware that collects RF voltage and current dataduring the operation of the system. This data is fed to adata-acquisition card (National Instruments DAQ 516) in a microprocessor14 (in a laptop computer), which then uses this voltage and current datato calculate the delivered power and load impedance. In addition to theanalog inputs required to monitor voltage and current, thisdata-acquisition card contains digital output channels which could beused to signal the stepper motor driver that the movement, i.e.,deployment and/or rotation sequence is to be initiated. FIG. 1 shows theelectrical interconnection of the components used in the system.

System Overview:

IO Controller 18: Additional signals need to be brought into the IOController 18, so that the motor deployment/rotation sequence can beinitiated once an arc has been detected. There are an additional twounused inputs on the Si5580 Stepper Motor Driver 19 that have been wiredto a unique connector 17 on the back panel of the controller 18. Thecircuit is shown in FIG. 2.

The operating software for the Si5580 drive unit 19 has been modified tocheck the status of these signals prior to starting the motor sequence.Once the arc detection routine has been completed, the “Detect RoutineComplete” signal is transmitted from the laptop computer 14 through theDAS Data Acquisition System 10 and to the Si5580 drive unit 19. Whenthis signal is received, and if the “Arc Initiated” signal is present,the deployment/rotation sequence is initiated. If an arc was notdetected, the “Detect Routine Complete” signal is generated absent the“Arc Initiated” signal, instructing the Si5580 drive unit 19 tode-energize the RF output and abort the remainder of the sequence. Inorder to permit the operation of the IO Controller 18 without the DASData-Acquisition System 10, the Si5580 drive unit 19 checks if the“Detect Routine Complete” signal is absent initially, in which case thesequence is initiated using the 400 millisecond delay, without using anyof the arc detection logic.

DAS Data-Acquisition System 10: As seen in FIG. 3, to electricallyisolate the DAS System 10 from the IO Controller 18, the digital signalson the DAQ 516 card 20 were connected to two ISOCOM optically coupledisolators 22, 24, which provide 5.3 kVRMS of electrical isolationbetween the input and output. Optically coupled isolators 22, 24 are ameans of transmitting a signal between two systems without having anydirect electrical connection. In this system, the signals of the DAQ 516cards 20 are connected to the inputs of the isolators and the outputs ofthe isolators are wired to a connector 30 on the enclosure, which isultimately connected to the IO Controller 18 and the inputs to theSi5580 drive unit 19. When the digital signals on the DAQ card 20 areactivated, a light emitting diode inside the isolator turns on, whichthen activates a photo-transistor on the output of the isolator. Thisphoto-transistor provides the signal to the Si5580 drive unit 19, whichallows light, rather than electrons, to become the transmission medium.This ensures that there is no possibility of any hazardous electricenergy being transferred from one system to the other.

The Visual Basic program used for data-acquisition from the DASController may be modified to check for an increase in impedance, whichindicates that an arc has started. What is unique about this approach inthe field of electrosurgery is the concept of monitoring the RF voltageand current output, thereby determining the load impedance (or othercharacteristic associated with the electrode) and using an observedchange in that load impedance to start an automated procedure. It wouldalso be possible to achieve a similar result by monitoring otherelectrical characteristics at the electrode, such as the deliveredcurrent or voltage, to determine when an arc has been initiated.

A review of the data files from bench and clinical testing indicatedthat typically the load impedance was below 400-450 ohms when theelectrode had not initiated an arc. Once an arc was initiated, the loadimpedance increased to at least 700 ohms, and in most cases exceeded1000 ohms. This information was taken into account to specify an initialvalue of, for example, 500 ohms as the threshold to determine when anarc has started. The software is preferably structured to allow the user(product designer) to alter this value to further refine the arcdetection scheme.

A timeout routine may be incorporated into the software as a safetyfeature. If the arc impedance threshold is not attained within, forexample, one second, indicating that an arc has not been created, the RFis de-energized, and the routine is aborted and the user is alerted ofthis fact.

There may be two digital signals used for the arc detection routine,“Detect Routine Complete” and “Arc Initiated”. When the softwaredetermines that an arc has been established, it sets the “Arc Initiated”signal high, and then indicates that the detection routine has completedby initiating a high-to-low transition of the “Detect Routine Complete”signal. This logic is structured in such a way as to minimize the riskof a false positive signal being sent to the controller, since it isunlikely that a single failure would cause both the “Arc Initiated”signal to be set high and the “Detect Routine Complete” signal to be setlow.

In another embodiment, as depicted in FIG. 4, the functionality of theRF (electrosurgical) generator 36, DAS 10, IO Controller 18, andmicroprocessor 14 is integrated into a single control unit 40. In yetanother embodiment, the control unit 50 contains a power supply 52, RF(electrosurgical) generator 36, controller 54, DAS 10, andmicroprocessor 14 (see FIG. 6). These integrated systems allow the motordrive sequence and RF output to be controlled by a single microprocessor14, which enhances the communication between the subsystems and allowadditional signal processing. With this type of integrated system, it ispossible to refine the control algorithms.

RF Output: With the other embodiment, the user sets the RF output poweron the commercially available generator at the start of the procedure.There is no provision for an automated adjustment of this RF outputpower, since there is no communication between the microprocessor 14 (inthe laptop computer) and the generator 36. With the integrated system ofthe preferred embodiment, however, it would be possible not just tosignal the motor drive system to start movement or rotation in responseto a change in load impedance, but it would also allow the RF output tobe adjusted to compensate for changes in load condition. In contrast toother methods, which vary the speed of the cutting electrode through thetissue in response to changes in the load impedance, varying the RFoutput is advantageous since the system responds faster electricallythan mechanically. With the preferred integrated system embodiment, thesystem monitors the performance during the automated sequence and makesadjustments during operation to reduce the incidence of failures. Forexample, if during the rotation sequence, the load impedance started tofall, the failure of the arc could be predicted, and the RF outputincreased in an effort to mitigate this failure. It would also allow thepotential for adjusting the RF output with respect to the position ofthe cut wire, as it is likely that the RF output requirement isdifferent at different points in the wire deployment/rotation sequence.As the cut process continues and as the sample is physically detachedfrom the bulk tissue, the electrical characteristics may change, and theperformance of the system could possibly be enhanced by makingadjustments to the output during rotation to compensate for thesechanges. This could also be employed to use a higher output power toestablish an arc, then cause the system to switch to a voltage controlmode, where the output voltage rather than power is regulated, once thewire deployment process is started. This type of control provides anadvantage, since a fixed output voltage causes the delivered power toincrease in response to a lower load impedance, and to decrease inresponse to a higher load impedance. In this fashion, when the arc iscreated, and the impedance increases, the power is automatically reducedto mitigate thermal damage.

The RF algorithm control includes the following steps:

1. Find baseline impedance—deliver low power (approximately 5 W) forapproximately 0.2-0.5 seconds and monitor load impedance, this sets abaseline value of impedance.

2. Initiate Arc—under power control, deliver high power output until anarc is detected by observing the load impedance increase approximately 2to 3 times above baseline, preferably approximately 2 times abovebaseline. The high power output can be in the range of approximately100-200 W. In a preferred embodiment, the high power output isapproximately 170 W.

3. Dwell approximately 25-150 ms, preferably approximately 40 ms,allowing for the arc to stabilize.

4. Deploy cut wire—switch to fixed output voltage and extend electrode.The fixed output may be in the range of approximately 200-350 V. In apreferred embodiment, the fixed voltage output should range fromapproximately 240-260 V.

5. Dwell approximately 0-150 ms, preferably approximately 20 ms,maintaining voltage control and allowing the arc to stabilize.

6. Start electrode rotation—deliver fixed output cut voltage. This maybe in the range of approximately 150-300 V, preferably 240-260 V.

7. Monitor impedance and recover arc if needed—monitor impedance andwhen it falls below approximately 2× the baseline value used in step 2,output approximately 170 W to re-initiate the arc. Alternatively, theoutput voltage could be increased to a higher, secondary level.

Motor Control: Using a single processor to control the RF output and themotor drive system also allows the motor speed to be regulated inresponse to changes in the load impedance. Different anatomicalstructures are comprised of different types of tissue, each of which hasdifferent electrical and physical properties. In general, there is arelationship between the density of the tissue and its electricalimpedance. Dense, fibrous tissue typically has a lower level ofhydration, which reduces its conductivity and increases its impedance.If this is taken into account, the arc detection system could also beused to regulate the speed of the motor drive system so that it isoptimized for the specific tissue encountered. For example, once an arcis created, it would be possible on dense tissues for the cuttingprocess to be further enhanced by slowing the speed of the electrode. Onspongy or fatty tissues, which are relatively easy to cut, the thermaldamage to the surrounding areas could be reduced by increasing the speedof the electrode, thereby minimizing the RF exposure. Furthermore, bymonitoring the status of the tissue electrical properties, the systemcould allow a dwell time at specific points in the sequence, which couldallow the arc to become more established and provide an improved cuttingeffect once motion is resumed. It could also determine if the arc at theelectrode dissipated, at which point the motor could be stopped and thearc initiation and detection routine repeated.

User Control

Handpiece: The reusable handpiece has two buttons on it for user controlof the system. One button is a “select” button that allows the user totoggle from one step of the procedure to the next. The other button isan “activate” button that allows the user to activate that step. Foruser convenience, the system also has an optional footswitch with twobuttons that function as “select” and “activate” under the same manneras the handpiece switches.

In operation, in one embodiment, the user may perform the followingsteps:

Home the reusable handpiece—This step moves the motors and themechanisms to a first position ready to receive the disposable insert.In particular, this step activates motor control to move the cut wiremechanism (CWM) and the Python/hook wire mechanism (PHWM) to a positionready to receive the disposable electrode insert.

Insert the disposable electrode—The user inserts the disposableelectrode into the reusable handpiece and secures it with a ¼ turnrotation. The disposable electrode has an ID resistor in it that thereusable handpiece detects and communicates to the control box. If theresistance value is within a certain range, the system automaticallyprograms itself for the proper disposable. The resistance value for a 15mm cut disposable electrode is different that the resistance value for a25 mm cut disposable electrode.

Ready for insertion—The disposable electrode comes with the capturePython and hook wire fully deployed. These are retracted into the shaftof the disposable electrode for device insertion into the patient.

Insertion—The user will create a skin incision to get the tip of thedevice under the skin. From there, the user gently pushes the devicetoward the intended target, e.g., a biopsy target. If tissue resistanceis felt, the user can activate the RF electrodes at the tip of theinstrument by tapping on the “activate” button. The details of thereusable handpiece, including the placement of the electrodes of thepenetrating tip, are described in related U.S. application Ser. No.10/374,582, filed on Feb. 25, 2003, entitled “Tissue Separating CatheterAssembly and Method,” the entirety of which is hereby expresslyincorporated by reference in its entirety.

Cut & capture sample—Once the device is in the proper position, the useractivates the cut and capture sequence. Holding down the “activate”button for the duration of the cut activates the following steps:sending RF energy to the electrode, detecting the arc, moving theelectrode, turning off the RF energy, stopping the electrode movement,and extending the hook wires and python. The user can also interrupt thecut sequence if desired.

Remove system from patient—The user withdraws the device with the cutsample from the patient.

Remove the sample from the device—The user hits the “activate” button tomake the Python and hook wire retract from the sample. Once withdrawn,the user can use forceps to remove the cut sample from the device.

Remove the disposable from the reusable—The user releases a springlatch, counter-rotates the disposable electrode by ¼ turn, and removesthe disposable electrode from the handpiece. The reusable handpiece canthen be homed for insertion of another disposable electrode.

In a preferred embodiment, the integrated control box allows the user tostart the cut sequence and stop it at any point. The user may elect tostop due to patient discomfort, or distraction in the room, etc. Byreleasing the “activate” button during the cut sequence, the RF energyis turned off and electrode movement stops. The system keeps track ofthe motor position to later re-activate and complete the movement. Torestart the movement, the user again holds down the “activate” buttonand the system will repeat the startup RF algorithm above from the placeit left off

Percutaneous devices can benefit from using an RF activated penetratingelectrode to ease placement. In yet another embodiment, RF energy isdelivered to the distal tip of the device, creating a small arc to makean incision during penetration. Typically, the activation periods ofsuch a device are very short, perhaps 500 to 1000 milliseconds. In thiscase, it is important to establish an arc as quickly as possible, but tominimize the power delivery in order to prevent damage to surroundingtissues. The same arc detection scheme could be employed to determinewhen an arc has been created, and then to limit the maximum power orvoltage delivered to the tissue. It could also be used to reduce thetime required to initiate an arc at the electrode, by delivering ahigher initial output power, which would then be reduced once the arcwas detected.

In another embodiment, a manually controlled system is used in whichcontrol of the electrosurgical electrode may be enhanced by monitoringand communicating feedback of a particular electrical characteristic tothe user during operation. Energy is first delivered to anelectrosurgical electrode to create an arc at that location, while theelectrode is stationary. The electrical characteristics associated withthe electrosurgical electrode are then monitored. The electricalcharacteristic being monitored may be any one, or a combination, of thefollowing: electrical impedance, a change in electrical impedance,voltage, a change in voltage, current, or a change in current. With amanually controlled electrode, once the creation of a cutting arc isestablished between the adjacent tissue and the electrode, the userinitiates movement of the electrode to effect separation of the tissuesection from the surrounding tissue. The electrical characteristic canbe continuously or periodically monitored and communicated to the userthroughout the cutting process. The user can then adjust the speed atwhich the electrode is being moved through the tissue based on theseelectrical characteristics.

In one embodiment, the RF generator signals to the user whether theelectrode movement should be faster to avoid excess tissue damage, orslower to avoid losing a good cutting arc. The user may receiveelectrical impedance feedback. An RF electrode will experience a shiftfrom low impedance, for example, about 100-300 ohms, when in directcontact with the tissue, to high impedance, after a cutting arc has beenestablished between the electrode and the tissue. Creation of a cuttingarc involves the current jumping from the electrode through a small airgap into the tissue. The minimum impedance value that is indicative ofthe creation of a weak cutting arc is about 600-1200 ohms. The lowarcing impedance values likely reflect arcing over a portion of theelectrode and direct conduction to tissue contact to the electrode overa portion of the electrode. Total load impedance can be as high as about2500-3000 ohms. Typically, the impedance values may be in the range of1500-2500 ohms, alternatively 1200-2500 ohms, alternatively 1200-3000ohms, alternatively 1500-3000 ohms.

After the cutting arc has been established, the RF generator for amanually operated system signals to the user that manual movement of thedevice should begin. During the excision, the RF generator signals theuser when the speed of the electrode should be increased or decreasedaccording to the electrical characteristic being monitored (e.g.,electrical impedance level). The RF generator signal to the user couldbe audio or visual. For example, the RF generator could emit a series ofsounds (e.g., beeps or chirps) that correspond to the level of theelectrical characteristic. In one embodiment, the speed at which thesounds are emitted could increase or decrease in accordance withelectrical characteristic (e.g., faster beeps may indicate a fasterspeed is needed). Alternatively, the pitch of the sound may varyaccordingly (e.g., a higher pitch may indicate a faster speed isneeded). In another embodiment, visual lights on the handpiece or the RFgenerator may signal to the user that an adjustment in speed is needed(e.g., different lights (see FIG. 6), different colored lights (notshown), or changing the frequency of blinking lights (not shown)).Alternatively, an analog or digital scale on the generator front panelor on an associated instrument may provide feedback to the user.

For minor fluctuations in the monitored impedance values, the systemcould be switched to a voltage control mode, where the output voltagerather than the power is regulated. As explained above, this type ofcontrol provides an advantage in that a fixed output voltage causes thedelivered power to increase in response to a lower load impedance, andto decrease in response to a higher load impedance. Accordingly, whenthe arc is created, and the impedance increases, the power isautomatically reduced to mitigate thermal damage. For largerfluctuations in the monitored impedance values, the user could use thefeedback systems described above and alter the speed of the electrodeaccordingly.

In some instances, the cutting arc may be extinguished during theprocedure. If this occurs, the electrical impedance would drop belowabout 500 ohms, or alternatively drops below about 2 times a baselineelectrical value, or alternatively drops below about 2.5 times abaseline electrical value. If the cutting arc has been extinguished, theuser should stop the rotation of the instrument, and then restart themethod by turning the RF power back on and detecting when the arc hasonce again been established before resuming rotation.

Although the foregoing invention has, for purposes and clarity ofunderstanding, been described in some detail by way of illustration andexample, it will be obvious that certain changes and modifications maybe practiced which will still fall within the scope of the appendedclaims.

1. A method for controlling the movement of an electrosurgical electrodeof an electrosurgical device within a target tissue comprising:inserting the electrosurgical electrode into the target tissue; movingthe electrode to a radially extended, outwardly bowed, operationalstate; initiating the delivery of energy to an electrosurgical electrodeto cut a target tissue; rotating the electrosurgical electrode;monitoring an electrical characteristic associated with theelectrosurgical electrode while rotating the electrosurgical electrode;and adjusting the energy delivered to the electrosurgical electrodebased upon the monitoring step so to at least help maintain an effectivearc.
 2. The method according to claim 1, wherein the monitoring step iscarried out by monitoring a change in electrical impedance.
 3. Themethod according to claim 1, wherein the monitoring step is carried outby monitoring a change in voltage.
 4. The method according to claim 1,wherein the monitoring step is carried out by monitoring a change incurrent.
 5. The method according to claim 1, wherein the monitoring stepis carried out by monitoring electrical impedance.
 6. The methodaccording to claim 1, wherein the monitoring step is carried out bymonitoring voltage.
 7. The method according to claim 1, wherein themonitoring step is carried out by monitoring current.
 8. The methodaccording to claim 5, wherein the monitoring step is carried out bymonitoring for an electrical impedance between about 700-1200 ohms. 9.The method according to claim 5, wherein the monitoring step is carriedout by monitoring for an electrical impedance value below about 700ohms.
 10. The method according to claim 5, wherein the monitoring stepis carried out by monitoring for an electrical impedance value belowabout 800 ohms.
 11. The method according to claim 5, wherein themonitoring step is carried out by monitoring for an electrical impedancevalue above about 1200 ohms.
 12. The method according to claim 1,wherein the rotating step comprises manually rotating theelectrosurgical electrode.
 13. The method of claim 1, further comprisingthe step of providing feedback to a user based upon the monitoring stepto adjust a speed of rotating the electrosurgical electrode.
 14. Themethod of claim 13, wherein the feedback to the user comprises audiofeedback.
 15. The method of claim 13, wherein the feedback to the usercomprises visual feedback.
 16. The method of claim 1, further comprisingthe step of monitoring the electrical characteristic to determine whenan arc has been initiated based upon the monitoring step before movingthe electrosurgical electrode.
 17. The method according to claim 16,wherein the monitoring step is carried out by monitoring for anelectrical impedance over 500 ohms.
 18. The method according to claim16, wherein the monitoring step is carried out by monitoring for anelectrical impedance value over 2-times a baseline electrical impedancevalue.
 19. The method according to claim 16, wherein the monitoring stepis carried out by monitoring for an electrical impedance value over2.5-times a baseline electrical impedance value.